1. Field of the Invention
The present invention relates to a chuck, or an extension useable with a chuck, for holding cutter or router bits.
2. Problems in the Art
Various machines are adapted for interchangeable tools. An example is a wood-working router. A chuck of the router is adapted to receive and fix a router bit shaft. There are a number of other types of machines that utilize such a chuck or an analogous structure.
The mechanism to fix the bit in the chuck must be durable and robust. It cannot allow longitudinal or rotational movement of the bit during operation, even when substantial forces are experienced by the working end of the bit. Any such movement would reduce the effectiveness of the tool or even be dangerous (e.g. a high speed bit could release and fly off).
A variety of methods exist for fixing a bit in a chuck. Standard designs for routers use arbor locks or factory two-wrench systems. Some examples can be seen in the following U.S. patents:
U.S. Pat. No. 3,091,474
U.S. Pat. No. 5,348,319
U.S. Pat. No. 5,096,212
U.S. Pat. No. 6,332,619
There are times when it is desirable to extend the working end of the bit from the machine. For example, in certain situations, it is desirable to extend the cutting or working end of a router bit farther from the factory chuck of the router than normal. A specific example is where the router is installed upside-down in a table, with the bit chuck at or near the table surface. Placing a standard router bit in the chuck extends the bit a distance above the table top. Even if there is some adjustability of the router or router chuck relative to the table top such that there can be some adjustment of the height of the bit above the table top, there are certain circumstances where it is desirable, or even necessary, that the working end of the router bit be higher than any available adjustment range of the bit in the normal chuck and router.
Although existing methods of fixing a bit in a chuck and allowing some adjustments of the chuck relative to a table top are adequate for many purposes, there still exists room for improvement in the art.
Attempts to extend the working end of the bit leave room for improvement in the art because of complexity in terms of manufacture or number of parts, and potential for failure or vibration. Many previous extensions use a standard threaded collet with an extended shank to extend the reach of the bit when needed. They are supplied with internal or external threaded means to compress either a nut or a peripheral set of moveable fingers, or a separate collet sleeve actuated by a nut threaded over the outside diameter of an extension body which, when tightened, compress the fingers of the sleeve onto the bit shank, thereby retaining it. These methods require the use of two wrenches or the arbor lock of the router to tighten and release the bit shank in the extension. They also added an extreme amount of length to the shank requiring substantial space to be fabricated to return the useable stroke of the router. Also, due to the extreme length and slim profile, they are prone to introducing a substantial amount of concentric rotating width into the spinning bit which creates vibration, both with the bit cutting and free running.
Therefore, an improved extension that deals with these problems is submitted to be needed in the art.
The above listed patents represent various ways of locking a bit shank into a chuck. They have the benefit of allowing single tool cutter changes without the use of the arbor locks or the factory two wrench system mentioned above. However, disadvantages of these designs include difficulty in manufacturing and inability to use standard and large shank bits. Also, the need for an individual chuck for each brand of router becomes apparent when the wide variety of collet designs used for each manufacturer are taken into account. These types of chucks also do nothing to extend the reach of the cutter when it is needed, such as on the Legacy Mill. Special extra-long bits are needed for these machines, which are hard to find and expensive when located.
Additionally, at least in U.S. Pat. Nos. 3,091,474 and 6,332,619, eccentric sleeves 26 and 209, respectively, are difficult to make and require extreme care by the user to ensure proper alignment and correct clamping. These sleeves are also oriented so that if the fastener should fail, the rotation of the bit shank will force the sleeve out of contact with the bit shank, thereby releasing the cutter from the machine. Other disadvantages to these designs are the difficulty of keeping the bore of the chucks concentric with the center line of the arbor due to the cone-shape formed on the bottom of the chuck to mate with the factory taper. Due to the clearance required to insert and remove the cutter when the bit is clamped in operating position, the center line of the bit is no longer concentric with the center line of the arbor on which it is mounted. They also have no means of retaining the bit in the chuck when used in a chuck-down vertical position. Assembly and repair is also hindered by the design of these chucks. The retention pins and spring rings used to hold the various components together are subject to catastrophic failure. If either the spring rings or the tension pins fail, the chucks are free to disengage from the arbor of the machine.
By referring to FIGS. 5 and 6 of U.S. Pat. No. 3,091,474, and FIG. 5 of U.S. Pat. No. 6,332,619, the eccentric nature of the sleeves is explicit. The bore through the sleeve is offset from the longitudinal axis of the sleeve.
U.S. Pat. No. 5,096,212 illustrates a clamping method using two sleeves 108 and 109 on a threaded screw 94 (See FIG. 17 of U.S. Pat. No. 5,096,212). This adds complexity and cost to that clamping system.
U.S. Pat. No. 5,348,319 utilizes a complex shaped member 12 inserted longitudinally into the chuck. Also a separate insert 16 is used to receive the bit shank 18. The complex shape 12 wedges against the exterior of collet 16 instead of the bit shank. This also is a complex arrangement and requires complex manufacturing of the chuck.
Vibration problems most acute with U.S. Pat. Nos. 3,091,474 and 6,332,619 cannot be machined out or calculated out because of the different bits and speeds used. Although the offset from the center line is relatively small, it can be enough to cause substantial vibration and unbalancing of the bit because the longitudinal axis of the shank of the bit is slightly offset from the longitudinal axis of the arbor.